Radio communication device, method, and program that calculate transmission time based on data rate

ABSTRACT

A radio communication method stores a plurality MAC frames for each of a plurality of destinations. The method decides the longest transmission time of transmission times needed to transmit the plurality of MAC frames to each of the plurality of destinations within a fixed period. The method generates a plurality of physical frames for the plurality of destinations to transmit them at the same time by connecting the plurality of MAC frames and adding additional information to each connected MAC frame so as to be a frame length equivalent to a transmission time equal to the longest transmission time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-339941, filed Dec. 28, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the invention relates to data transmissions when datais simultaneously transmitted to a plurality of radio communicationdevices in the case where a plurality of radio communication devicesexist.

2. Description of the Related Art

A multi-user Multiple Input Multiple Output (MIMO) has been recognizedas a method for simultaneously performing MIMO communication among radiocommunication terminals of a plurality of users at the same time and inthe same frequency band through evolution of a MIMO technique. While themulti-user MIMO communicates at the same time and in the same frequencyband, it is impossible to perform transmissions and receptions at thesame time. That is, while the multi-user MIMO may perform a plurality ofMIMO transmissions at the same time in the same frequency band, it ispresently impossible to simultaneously perform reception. Conversely,while a plurality of MIMO receptions may be performed at the same timeand in the same frequency band, it is presently impossible tosimultaneously perform transmission. It is impossible to separatetransmissions and receptions from each other when they occur at the sametime in a terminal. Therefore, in the multi-user MIMO, there is a needto separate transmission times from reception times.

As regards a technique for separating the transmissions from thereceptions, for example, a technique of adjusting the timing oftransmissions of transmission acknowledgement request frames (AckRequests) so as to make the reception times of transmissionacknowledgement frames (Acks) from a plurality of radio communicationdevices uniform when a plurality of frames differing in transmissiontime have been transmitted to the corresponding plurality of radiocommunication devices is disclosed in U.S. Patent ApplicationPublication No. 2005/0147023. However, since the technique described inthis patent document contains the transmissions of the Ack Requests asessential elements, overheads of times for transmitting the Ack Requestsare generated, and this generation might lead to deterioration inthroughput. In the case in which the Ack Requests are judged as errorsowing to a radio environment and may not be received on receptionterminal sides, even if transmission data has reached them, there is aneed to retransmit the transmission data for the Ack Requests. Thisretransmission might lead to deterioration in throughput.

As regards another technique for separating the transmissions from thereceptions, in the case in which one piece of data is divided and datatransmission is performed by using a plurality of transmission channelsat the same time, controlling the number of bytes of data frames to bedivided to uniform transmission times of the data frames is disclosedin, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-350259.However, the technique described in this patent document does not takeany account of combining a plurality of data frames to transmit themwhen a plurality of data frames are stored in a transmission queue,i.e., transmitting the data frames by a frame aggregation system asdescribed in IEEE 802.11n. In other words, in the technique described inthe patent document, it is impossible to combine the transmissions ofthe data frames with a radio transmission system, such as the frameaggregation system in IEEE 802.11n, at a high rate and with highefficiency. In IEEE 802.11n, by which a standardization proposal is madeas a radio communication technique at a high rate by the MIMO technique,a frame aggregation technique for combining a plurality of medium accesscontrol (MAC) frames into one physical (PHY) frame to transmit the PHYframe has been proposed as a technique of a MAC layer corresponding toacceleration of the PHY layer (e.g., refer to IEEE 802.11/D2.00).

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a radiocommunication device, comprising: a storage unit which stores aplurality of MAC frames for each of a plurality of destinations; adecision unit which decides the longest transmission time oftransmission times needed to transmit the plurality of medium accesscontrol (MAC) frames for each of the plurality of destinations within afixed period; a connection unit which connects the plurality of MACframes; an addition unit which adds additional information to MAC frameseach connected so as to be a frame length equivalent to a transmissiontime equal to the longest transmission time; a generation unit whichgenerates a plurality of physical frames from the plurality of theconnected MAC frames to which the additional information is added so asto be the frame length; and a transmission unit which transmits theplurality of physical frames at the same time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exemplary block diagram depicting a configuration of awireless LAN device of an embodiment of the invention;

FIGS. 2A and 2B are exemplary flowcharts depicting operations of thewireless LAN device of an embodiment of the invention;

FIG. 3 is an exemplary view depicting an example of frame exchanges inthe case in which transmission times of transmission frames are notadjusted;

FIG. 4 is an exemplary view depicting an example of frame exchangeswherein an A-MAC Protocol Data Unit (MPDU) system of IEEE 802.11n iscombined with multi-user MIMO communication by a wireless LAN device ofa first embodiment;

FIG. 5 is an exemplary view depicting an example of frame exchangeswherein an A-MPDU system of IEEE 802.11n is combined with multi-userMIMO communication by a wireless LAN device of a second embodiment;

FIG. 6 is an exemplary view depicting an example of frame exchangeswherein an A-MPDU system of IEEE 802.11n is combined with multi-userMIMO communication by a wireless LAN device of a third embodiment;

FIG. 7 is an exemplary view depicting an example of frame exchangeswherein an A-MPDU system of IEEE 802.11n is combined with multi-userMIMO communication by a wireless LAN device of a fourth embodiment;

FIG. 8 is an exemplary view depicting an example of frame exchangeswherein an A-MPDU system of IEEE 802.11n is combined with multi-userMIMO communication by a wireless LAN device of a fifth embodiment; and

FIG. 9 is an exemplary view depicting an example of frame exchangeswherein an A-MPDU system of IEEE 802.11n is combined with multi-userMIMO communication by a wireless LAN device of a sixth embodiment;

DETAILED DESCRIPTION OF THE INVENTION

Concrete embodiments of the invention will be described based on awireless LAN communication system of IEEE 802.11. However, the wirelessLAN communication system in IEEE 802.11n is only an example of a radiocommunication system to which an effect of the invention is applicable;i.e., the invention is also applicable to other radio communicationsystems. In the description hereinafter, a radio base station isreferred to as an “access point (AP)”, and a radio terminal or a radiocommunication device to be connected to the AP is referred to as a“station (STA)”.

(First Embodiment)

A wireless LAN device 101 of the embodiment as shown in FIG. 1 comprisesa transmission Queue 106 storing transmission data; a Queue Control unit107 controlling a transmission destination and the number of items oftransmission data from a data storage situation of the Queue 106; a rateselection unit 108 deciding a transmission rate of a PHY layer byselecting any one of a prescribed plurality of transmission rates inresponse to a propagation environment; an aggregation processing unit105 performing connection processing when a plurality of items oftransmission data are connected to one frame and transmitting the frame;and a plurality of transmission and reception processing units 102, 103,104 transmitting and receiving a plurality of streams by means of MIMOcommunication or multi-user MIMO communication.

The aggregation processing unit 105 includes a connection unit 1052connecting a plurality of MAC frames; an addition unit 1053 addingadditional information to the MAC frames each connected by theconnection unit 1052 so as to be a frame length equivalent to atransmission time equal to the longest transmission time to bedetermined by the Control unit 107; and a generation unit 1054generating a plurality of physical frames for the plurality ofdestinations from the connected plurality of MAC frames to whichadditional information is added so as to be of a frame length.

According to the plurality of processing units 102, 103, 104, the LANdevice 101 may transmit a plurality of streams of the MIMO communicationcapable of transmitting a plurality of streams at the same time and inthe same frequency band. That is, the LAN device 101 may performmulti-user MIMO communication; however even when adopting acommunication system using a plurality of channels (multi-channel) totransmit the streams to a plurality of different channels at the sametime, the processing units 102, 103, 104 are applicable.

In IEEE 802.11n, an A-MAC Service Data Unit (A-MSDU), which is afunction for performing aggregation in MSDU units, and an A-MAC ProtocolData Unit (A-MPDU), which is a function for performing aggregation inMPDU units, are proposed. In A-MSDU, since one Header is added to aplurality of units, redundant headers may be reduced and thetransmission time may be reduced, throughput may be improved, and powerconsumption saving may be achieved. In the A-MPDU, overhead parts suchas a PHY header, Preamble SIFS time and an ACk frame added to each of aplurality of MPDU transmissions may be reduced, redundant transmissiontimes may be reduced to improve the throughput, and power consumptionsaving may be achieved. While the embodiment will describe the case ofperforming the A-MPDU of IEEE 802.11n as an example, the invention maybe implemented in the case of adoption of other aggregation systems.

Operations of the wireless LAN device 101 of the embodiment will bedescribed with reference to FIGS. 2-4. More specifically, the case inwhich the LAN device 101 performs data transmission processing to threeSTA 1, STA 2, STA 3 as transmission destinations will be described, asan example.

When the LAN device 101 generates the transmission data, thetransmission data is stored in the transmission Queue 106 (Step 1). TheQueue Control unit 107 decides the transmission destinations STA 1, STA2, STA 3 and transmission channels from data information stored in theQueue 106 (Step 2). The Queue Control unit 107 notifies the transmissiondestinations and the decided transmission cannels to the rate selectionunit 108.

The selection unit 108 recognizes a propagation situation of radiopackets in transmission passages and decides the transmission rate andthe maximum value of transmittable times on the basis of the propagationsituation (Step 3). The maximum value of the transmittable times isobtained by calculating how long the transmission times become at amaximum depending on the propagation situation. As regards the maximumvalue of the transmittable time, a Transmission Opportunity (TXOP) Limit(a limit of channel use period) may be used.

The Control unit 107 collects information of the maximum transmissiontime for each transmission destination from the selection unit 108 (Step4). Here, it is determined whether or not the individual maximumtransmission times are equal to one another in transmitting thetransmission data to streams or channels differing for each destination(Step 5). If each maximum transmission time differs, the shortest timeis decided as the maximum transmission time (T1) for all streams (Step6). Meanwhile, if the maximum transmission times of all streams areidentical, this time is decided as the maximum transmission time (T1)for all streams (Step 7).

After deciding the time (T1), the Control unit 107 obtains the number ofitems of the transmittable data which is transmittable within the time(T1) from a storage amount and a transmission rate for each transmissiondestination STA 1, STA 2, STA 3 (Step 8). The embodiment shows the casein which the transmission Queue 106 stores a sufficiently large amountof transmission data. The case of a small data storage amount will bedescribed in another embodiment.

Further, the Control unit 107 calculates transmission times of framesupon transmitting from each stream by combining the A-MPDU system ofIEEE 802.11n with the multi-user MIMO communication from the number ofthe items of the transmission data decided in Step 8 and thetransmission rate decided in Step 3 (Step 9).

The Control unit 107 determines whether or not the transmission times ofthe transmission frames to be transmitted from the respective streamsare equal to one another (Step 10). As a result of mutual comparison oftransmission times of the respective transmission frames, if thetransmission times of all streams are equal to one another, the Controlunit 107 performs transmission processing (Step 13).

However, usually, the respective stream may have different data lengths,numbers of pieces of transmission data, or transmission rates of thetransmission data to be transmitted from the respective streams by theLAN device 101. Therefore, it is not frequent for the transmission timesof the transmission frames to be transmitted from all streams to beequal to one another in Step 10.

If the transmission times of the transmission frames to be transmittedfrom all streams are different from one another, the Control unit 107decides the longest transmission time (T2) (Step 11).

For instance, if a transmission time of a frame f2 to be transmitted toa second radio communication stream become the longest one as shown inFIG. 3, that is, if a transmission time of a frame f1 to be transmittedto a first radio communication stream and a transmission time of a framef3 to be transmitted to a third radio communication stream transmissionis shorter than the transmission time of the frame f2 to be transmittedto the second radio communication stream, the transmission time (T2) ofthe frame f2 to be transmitted to the second radio communication streamis extracted.

The connection unit 1052 generates a frame by connecting MPDUs (MACframes) read from the transmission Queue 106. The addition unit 1053adds a certain piece of redundant information (additional information)so that the transmission time of the frame f1 to be transmitted to thefirst radio communication stream and the transmission time of the framef3 to be transmitted to the third radio communication stream becomeequivalent to the transmission time (T2) of the frame f2 to betransmitted to the second radio communication stream (Step 12).

More specifically, the addition unit 1053, for example, as shown in FIG.4, connects an MPDU Delimiter in the A-MPDU system, which has beenproposed in IEEE 802.11n, to each of the last tail of the frame f1 forthe first radio communication stream and the last tail of the frame f3for the third radio communication stream. One of the MPDU Delimiters(MPDU connection information field) is, for example, a fixed length, andthe frame length is adjustable by connecting a plurality of the MPDUDelimiters each having the fixed length. In FIG. 4, a frame formed byconnecting an MPDU Delimiter d1 (formed of six MPDU Delimiters) to theframe f1 of FIG. 3 is indicated as a frame f1′, and a frame formed byconnecting an MPDU Delimiter d3 (formed of three MPDU Delimiters) to theframe f3 of FIG. 3 is indicated as a frame f3′.

Therefore, as is clear from FIG. 4, the transmission time of the framef1′ to be transmitted to the first radio communication stream and thetransmission time of the frame f3′ to be transmitted to the third radiocommunication stream become equal to the transmission time T2 of theframe f2 to be transmitted to the second radio communication stream.Thus, adjusting is implemented so that the transmission times of theframes of the respective streams become equal to one another. Thegeneration unit 1054 generates a plurality of physical frames for aplurality of destinations (wherein differences in destination areequivalent to differences in stream). The transmission and receptionprocessing units 102, 103, 104 transmit each of the plurality of framesgenerated from the generation unit 1054 at the same time and thentransmit to all streams at the same time (Step 13).

The case in which the aforementioned adjustment of the frametransmission times of the embodiment of the invention is not implementedwill be described by referring to FIG. 3. In this case, during thetransmission of the frame f2 to the second radio communication stream,the need to receive Block Ack (block transmission acknowledgement: BA)frames 301, 303 returned from the STA 1 and the STA 3, respectively, isposed. In the case in which the transmission processing and thereception processing cannot be performed at the same time in themulti-user MIMO system, even the different streams of the plurality ofstreams may not establish the communication, as is shown in FIG. 3.

Conversely, in the case of using the method of the embodiment of theinvention, the adjustment is carried out so that the transmission timesof the transmission frames to be transmitted from the respective streamsbecome equal to one another. Therefore, transmission completion times ofthe respective frames become uniform after the completion of thetransmission processing to all streams, and the radio communicationdevice 101 can receive Block Ack frames 401, 402, 403 returned from STA1, STA2, and STA 3, as is shown in FIG. 4.

It is not necessary for receiving the Block Ack frames 401, 402, 403 atstrictly the same time. There is a case in which the transmission timesof the transmission frames of the respective streams cannot be perfectlyuniform with one another, in such a case; it is sufficient if thedeviance of the transmission times is suppressed within an SIFS time.Anyway, it is sufficient if occurrences of the transmission processingand the reception processing at the same time can be avoided.

A connection method for the MPDU Delimiters in the case of the use ofthe MPDU Delimiters so as to make the transmission time of thetransmission frame equivalent to the transmission time of the specifiedframe will be described.

While the former IEEE 802.11n standards have defined a transmission of asingle MPDU Delimiter (MAC frame), in IEEE 802.11n, a plurality of MPDUsare combined into one frame to create the A-MPDU frame, and such anA-MPDU frame transmits a plurality of MPDUs at the same time. At thismoment, the wireless LAN device adds the MPDU Delimiters at Heads of therespective MPDUs, and frame lengths of the MPDUs connected just afterare described in MPDU length fields in the MPDU Delimiters to set themas identifiers when the respective MPDUs are separated.

In the embodiment, to uniform the transmission times of the transmissionframes of the respective streams, the addition unit 1053 connects onlythe MPDU Delimiters (d1, d3) not including the following MPDUs, as shownin FIG. 4.

Accordingly, in the embodiment, it becomes possible to make thetransmission times of the transmission frames of the respective streamsequivalent to one another without going counter to the A-MPDU system inIEEE 802.11n.

Even when the wireless LAN communication standard in the multi-user MIMOsystem for performing the MIMO communication with the plurality of userMIMO terminals at the same time and in the same frequency band while,for instance, the wireless LAN device 101 operates as an access point,and synchronizes with each of the plurality of user MIMO terminals to beaccommodated at the access point is established as new standards afterIEEE 802.11n, according to the transmission system of the embodiment ofthe invention, backward compatibility may be maintained as mentionedbelow.

For instance, although the LAN device 101 establishes the communicationin the multi-user MIMO system, the LAN device 101 assumes a situation inwhich wireless LAN terminals compatible with IEEE 802.11n standardssupporting the MIMO communication but not supporting the multi-user MIMOsystem are included in the plurality of the transmission destinationterminals. For instance, the STA 3 is assumed to be a wireless LANterminal compatible with such an IEEE 802.11n in FIG. 4. In thisembodiment of the invention, after connecting the plurality of MPDUs,the wireless LAN device adjusts the transmission times of thetransmission frames in the method compatible with the A-MPDU system inIEEE 802.11n. More specifically, the LAN device describes zero in theMPDU length field in the MPDU Delimiter to make the connections and thenadjusts the transmission times. Therefore, the STA 3 that is thewireless LAN terminal which is compliant with IEEE 802.11n standards maynormally receive the frames through the reception processing based onIEEE 802.11n standards.

The STA 3 that is the wireless LAN terminal which is compatible withIEEE 802.11n standards also may operate the multi-user MIMOcommunication terminal with the intention of delaying the return time ofthe Block Ack in the multi-user MIMO communication. Accordingly, themulti-user MIMO communication may maintain the backward compatibilitywith IEEE 8023.11n standards.

While the embodiment has described the radio communication in themulti-user MIMO system using the plurality of streams, the radiocommunication method to which the invention can be applied is notlimited only to the multi-user MIMO system. The invention is alsoapplicable to a communication form in a multi-channel environment inwhich a plurality of radio channels are used in the same way as that ofthe plurality of streams of the embodiment.

As mentioned above, according to the embodiment of the invention, in themulti-user MIMO communication and in the multi-channel communication,the wireless LAN device may efficiently separate the transmission timesfrom the reception times. Since the frame aggregation technique is used,the throughput is not deteriorated. Further, the backward compatibilitywith IEEE 802.11n standards may be maintained.

(Second Embodiment)

Since a second embodiment is a modified example of the first embodiment,parts differing from those of the first embodiment will be mainlydescribed. The second embodiment differs from the first embodiment in amethod for adjusting frame transmission times. The configuration of awireless LAN device of the second embodiment is the same as that shownin FIG. 1, which has been described in the first embodiment. Operationsof the LAN device of this embodiment are the same as those of the firstembodiment from Step 1 to Step 11 of FIG. 2. That is, also in the secondembodiment, it is assumed that the transmission time of the frame 2 forthe second radio communication stream in FIG. 2 is extracted as thelongest transmission time (T2) (Step 11). At this moment, as is shown inFIG. 1, the transmission time of the frame f1 to be transmitted to thefirst embodiment and the transmission time of frame f3 to be transmittedto the third radio communication stream have become shorter than thelongest transmission time T2 in accordance with the difference in theMPDU length of each stream, and in the number of storages andtransmission rates of the transmission Queue 106.

As shown in FIG. 5, also in the second embodiment, to uniform thetransmission times in the same way as in the first embodiment, theaddition unit 1053 adds the MPDU Delimiter behind the last MPDU of eachpiece of the transmission data; however especially in the secondembodiment, the number of the MPDU Delimiters to be added is set to “1”,and following the MPDU Delimiters, and connects Quality of Service (QoS)Null frames to uniform the transmission times (Step 12).

Therefore, as is clear in FIG. 5, a transmission time of a frame f1 a tobe transmitted for the first radio communication stream and atransmission time of a frame f3 a to be transmitted for the third radiocommunication stream become equal to the transmission time T2 of theframe f2 to be transmitted for the second radio communication stream.Thus, after adjusting so that the transmission time of the frame to eachstream becomes equal, all streams are transmitted at the same time (Step13).

The QoS Null frame defined by the existing IEEE 802.11e has a fixedlength having a MAC Header and a cyclic redundancy code (CRC). Leavingthe QoS Null frame as it is, if the frame lengths of the first and thethird radio communication streams are different from each other, theframe transmission times may not be uniformed. Therefore, as shown inFIG. 5, a Frame Body 502 is inserted for padding between a Header 501and a CRC 503, and the length of the Frame Body 502 is made variable.Thereby, even if the transmission times of the respective streams areuneven, using such a QoS Null frame which is variable in length enablesadjusting the transmission times of the frames.

In a method of the second embodiment, even if the length of the FrameBody is set to zero, the addition of the QoS Null frame makes the framelong in length, and poses the possibility of the case in which thetransmission time of the frame exceeds the longest transmission time(T2). At this time, if the transmission times of the frames are notlonger than the length of transmittable time (T1) for all streams, thevalue of the transmission times of the frames are redefined to T2. It ispreferable to adjust the transmission times of the transmission framesin all streams so that the transmission times become equal to the newlydefined longest transmission time T2. If the transmission times of thetransmission frames of all frames exceed the longest transmittable time(T1), a method can be used, which should not use the QoS Null frame, butmay connect the MPDU Delimiters in the same way as the first embodimentand uniform the transmission times.

Even in the aforementioned second embodiment, similarly to the abovefirst embodiment, in the communication using the multi-user MIMOcommunication and the communication using the multi-channel, thewireless LAN device may efficiently separate the transmission times andthe reception times without causing deterioration in throughput, and maymaintain the backward compatibility with IEEE 802.11n standards.

(Third Embodiment)

Since a third embodiment is a modified example of the first embodiment,the third embodiment will mainly describe parts differing from those ofthe first embodiment. The third embodiment is different from the firstembodiment in a method for adjusting the frame transmission times. Aconfiguration of a wireless LAN device of this embodiment is the samethat is shown in FIG. 1 described in the first embodiment. Operations ofthe LAN device of this embodiment are the same as those of the firstembodiment from Step 1 to Step 11 of FIG. 2. That is, also in the thirdembodiment, it is assumed that the transmission time of the frame 2 forthe second radio communication stream in FIG. 2 is extracted as thelongest transmission time (T2) (Step 11). At this moment, as is shown inFIG. 3, the transmission time of the frame f1 to be transmitted for thefirst embodiment and the transmission time of frame f3 to be transmittedfor the third radio communication stream have become shorter than thelongest transmission time T2 in accordance with the difference in theMPDU length of each stream, and in the number of storages andtranslation rates of the transmission Queue 106.

As shown in FIG. 6, even in the third embodiment, similarly to the firstembodiment, to uniform the transmission times, the addition unit 1053adds the MPDU Delimiter behind the last MPDU of each piece oftransmission data; however, especially in the third embodiment, for theframes for the first radio communication stream, makes a copy of an MPDU3 that is the last MPDU in the A-MPDU, adds the MPDU Delimiter, and addsa copy 601 of the MPDU behind the A-MPDU to form a frame f1 b.

In this embodiment, as is clear from FIG. 6, in the first radiocommunication frame, the transmission time of the frame f1 b becomeslonger than the longest transmission time (T2). If the transmission timeof the frame f1 b is not longer than the maximum transmission time (T1)for all streams, the value of the transmission time of the frame f1 b isredefined as T2.

As regards the second radio communication stream, the addition unit 105adjusts the transmission times of the frames so as to make thetransmission times of the frames equal to the newly defined transmissiontime T2 by connecting a plurality of MPDU Delimiters d5 to the frames,and then, forms the frame f2 b. As regards the third radio communicationstream, the addition unit 105 adjusts the transmission times of theframes so as to make the transmission times of the frames equal to thenewly defined transmission time T2 by connecting a plurality of MPDUDelimiters d6 to the frames, and then, forms the frame f3 b. Thereby,the transmission times of all streams are uniformed (Step 12).

Thus, after adjusting the transmission times so as to uniform thetransmission time of the frame of each stream, the transmissionprocessing is performed for all streams at the same time (Step 13).

A method may be used which uniforms the transmission times by connectingthe MPDU Delimiters in the same way as that of the first embodimentwithout adding the copy 601 of the MPDU if the transmission time of theframe f1 b exceeds the maximum transmission time (T1) for all streams.

Also in the above third embodiment, similarly to the aforementionedfirst embodiment, in the communication using the multi-user MIMOcommunication and the communication using the multi-channel, thewireless LAN device does not pose the danger of deterioration inthroughput, and may efficiently separate the transmission times and thereception times. Further, the LAN device may maintain the backwardcompatibility with IEEE 802.11n standards.

(Fourth Embodiment)

Since a fourth embodiment is a modified example of the first embodiment,the fourth embodiment will mainly describe the parts differing fromthose of the first embodiment. The fourth embodiment is different fromthe first embodiment in a method for adjusting the frame transmissiontimes. A configuration of a wireless LAN device of this embodiment isthe same that shown in FIG. 1 described in the first embodiment.Operations of the LAN device of this embodiment are the same as those ofthe first embodiment from Step 1 to Step 10 of FIG. 2, That is, also inthe fourth embodiment, it is assumed that the transmission time of theframe 2 for the second radio communication stream in FIG. 2 is extractedas the longest transmission time (T2) (Step 11). At this moment, as isshown in FIG. 3, the transmission time of the frame f1 to be transmittedto the first embodiment and the transmission time of frame f3 to betransmitted to the third radio communication stream have become shorterthan the longest transmission time T2 in accordance with the differencein the MPDU length each stream, and in the number of storages andtranslation rates of the transmission Queue 106.

As shown in FIG. 7, also the fourth embodiment adjusts the timetransmissions similarly to the first embodiment. Especially in thefourth embodiment; however, as regards the frames for the first radiocommunication stream, the addition unit 1053 inserts a plurality of MPDUDelimiters d8 in front of the last MPDU (namely, MPDU 3) in theplurality of MPDUs and forms the frame f1 c. Thereby, the wireless LANdevice makes the transmission time of the frame f1 to be transmitted tothe first radio communication stream and the transmission time of theframe f3 c to be transmitted to the third radio communication streamuniform with the transmission time (T2) of the frame f2 to betransmitted to the second radio communication stream (Step 12).

Thus, after adjusting the transmission time of the frame of each streamto be uniform with one another, the transmission processing is performedfor all streams at the same time (Step 13).

According to the fourth embodiment, by using the MPDU Delimiters, thewireless LAN device may uniform the transmission time of each streamwhile maintaining the backward compatibility with IEEE 802.11nstandards, and also may uniform the transmission completion time of theMPDU to be transmitted from each stream.

Thus, the wireless LAN device may return Block Ack frames 701, 702, and703 that are transmission acknowledgement frames from the transmissiondestination terminal of each stream at the same time.

(Fifth Embodiment)

Since a fifth embodiment is a modified example of the fourth embodiment,the fifth embodiment will mainly describe parts differing from those ofthe first and the fourth embodiments. The fifth embodiment is differentfrom the first embodiment in a method for adjusting the frametransmission times. A configuration of a wireless LAN device of thisembodiment is the same as that shown in FIG. 1 described in the firstembodiment. Operations of the LAN device of this embodiment are the sameas those of the first embodiment from Step 1 to Step 10 of FIG. 2. Thatis, also in the fifth embodiment, it is assumed that the transmissiontime of the frame 2 for the second radio communication stream in FIG. 2is extracted as the longest transmission time (T2) (Step 11). At thismoment, as is shown in FIG. 3, the transmission time of the frame f1 tobe transmitted to the first embodiment and the transmission time offrame f3 to be transmitted to the third radio communication stream havebecome shorter than the longest transmission time T2 in accordance withthe difference in the MPDU length of each stream, and in the number ofstorages and translation rates of the transmission Queue 106.

As shown in FIG. 8, also in the fifth embodiment, similarly to thefourth embodiment, although the wireless LAN device adjusts the timetransmissions, especially in the fifth embodiment, as regards the firstradio communication stream, the addition unit 1053 inserts the samenumber of MPDU Delimiters as in the fourth embodiment so as to leave aspace of an SIFS period or an RIFS period in front of an MPDU Delimiterd10 immediately in front of the last MPDU 3. Thereby, the LAN deviceseparates the A-MPDU frame having the MPDU 1 and the MPDU 2 from thelast MPDU 3, and transmits two physical frames; a frame f1 d 1 and aframe f1 d 2, respectively. Also, as regards the second radiocommunication stream in a similar way, the addition unit 1053 leaves aspace of the SIFS period or the RIFS period in front of an MPDUDelimiter d13 immediately in front of the last MPDU 3. Thereby, the LANdevice transmits the frames as a frame f2 d 2 having the MPDU 1 and theMPDU 2, and as a frame f2 d 2 having the MPDU 3. As regards the thirdradio communication stream, in a similar way, the addition unit 1053leaves a space of the SIFS period or the RIFS period in front of am MPDUDelimiter d12 immediately in front of the last MPDU 2. Thereby, the LANdevice transmits the frames as a frame f3 d 1 having the MPDU 1 and theMPDU Delimiter d11 and as a frame f3 d 2 having the MPDU 2.

In the fifth embodiment, aggregation frames including a plurality ofMPDUs in the A-MPDU system may use physical frames (e.g., frame f1 d 2,f2 d 2, f3 d 2) of the space of the SIFS period or the space of the RIFSperiod, and may be configured of frames not including the MPDUDelimiters so as to transmit the stream including only MPDUs.

Since the A-MPDU system connects and transmits a plurality of MPDUs, theframe length thereof becomes long, resulting in the problem of apossibility of transmission errors in the latter half of the frameincreases. To avoid this problem, while the conventional A-MPDU systemcontrols so that the frame length thereof does not become longer than aprescribed length, in this embodiment, separating the MPDU into two ormore physical frames enables avoiding the problem that the latter halfof the frame in the S-MPDU system leads to a transfer error.

Thus, after adjusting the streams so as to uniform the transmissiontimes of the frames of the respective streams, the LAN device transmitsall streams at the same time (Step 13).

According to the fifth embodiment, using the MPDU Delimiters enablesuniforming the transmission times of the respective streams whilemaintaining the backward compatibility with IEEE 802.11n, and alsoenables uniforming the transmission completion times of the MPDUs to betransmitted from the respective streams. Therefore, it makes it possibleto return at the same time Block Acks 801, 802 and 803 that aretransmission acknowledgement frames from transmission destinationterminals of the respective streams.

Further, according to the fifth embodiment, since the plurality of MPDUsmay be separated into two or more physical frames, the wireless LANdevice may lengthen the transmission time of each stream whilepreventing the problem such that the physical frame length becomes long,which increases the possibility of transmission errors.

(Sixth Embodiment)

Since a sixth embodiment is a modified example of the first embodiment,the sixth embodiment will mainly describe parts differing from those ofthe first embodiment. The sixth embodiment is different from the firstembodiment in a method for adjusting the frame transmission times. Aconfiguration of a wireless LAN device of this embodiment is the same asthat shown in FIG. 1 described in the first embodiment. Operations ofthe LAN device of this embodiment are the same as those of the firstembodiment from Step 1 to Step 10 of FIG. 2. That is, also in the sixthembodiment, it is assumed that the transmission time of the frame 2 forthe second radio communication stream in FIG. 2 is extracted as thelongest transmission time (T2) (Step 11). At this moment, as is shown inFIG. 3, the transmission time of the frame f1 to be transmitted to thefirst embodiment and the transmission time of frame f3 to be transmittedto the third radio communication stream have become shorter than thelongest transmission time T2 in accordance with the difference in theMPDU length of each stream, and in the number of storages andtranslation rates of the transmission Queue 106.

Also in the sixth embodiment, similarly to the first embodiment, whilethe addition unit 1053 connects the MPDU Delimiters in the A-MPDU systemproposed in IEEE 802.11n to the last tail of the frame in the firstradio communication stream and the last tail of the frame in the thirdradio communication stream, respectively, especially in the sixthembodiment, the addition unit 1053 connects Block Ack Request (blocktransmission acknowledgement request) frames 901 and 902 to the lasttail of the frame in the first radio communication stream and the lasttail of the frame in the third radio communication stream, respectively.Thereby, the transmission times of all the streams are uniformed (Step12).

In the sixth embodiment, similarly to the fifth embodiment, the additionunit 1053 may leave the space of the SISF period or the RIFS period infront of the last MPDU or the MPDU Delimiters immediately in front of aBAR. The wireless LAN device may perform transmission processing as twophysical frames separating the A-MPDU frame from the LAST MPDU or theBAR. In this case, an aggregation frame including a plurality of MPDUsin the A-MPDU system may be used, and a stream may be configured asframes not including any MPDU Delimiter so as to transmit the streamonly by the MPDU. The A-MPDU system has the problem that the framelength becomes long because of transmission involving connecting aplurality of MPDUs; as a result, the possibility of transmission errorsin the latter half of the frame increases. To avoid this problem,conventionally, the frame length in the A-MPDU system is controlled soas not to become longer than a prescribed length, thus it becomespossible to avoid the problem that the latter half of the frame in theA-MPDU system e transmission error by separating the frame into two ormore physical frames.

Thus, after adjusting so as to uniform the transmission times of theframes for the respective streams, the transmission processing for allthe streams is performed at the same time (Step 13).

According to the sixth embodiment, using the MPDU Delimiters enableuniforming the transmission times of the respective streams whilemaintaining the backward compatibility with IEEE 802.11n standards, andalso enables uniforming transmission completion times of a BAR 901 of aframe f1 e to be transmitted from the first radio communication stream,of a MPDU 3 of a frame f2 to be transmitted from the second radiocommunication stream, and of a BAR 902 of a frame f3 e to be transmittedfrom the third radio communication stream.

Accordingly, it makes it possible to return Block Ack frames 903, 904,and 905 that are transmission acknowledgement frames from transmissiondestination terminals of the respective streams at the same time.

Further, the sixth embodiment makes it possible to lengthen thetransmission times of the respective streams while preventing theproblem that the lengths of the physical frames become long and thepossibility of transmission errors increases when the plurality of MPDUsare composed of two or more physical frames.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A radio communication method, comprising:connecting a set of MAC frames into a first unit, the set of MAC frameshaving a same destination; calculating each of a plurality of secondtransmission times based on a length of the first unit and a data rate,the first unit and the data rate corresponding to one of a plurality ofphysical frames, the plurality of physical frames being transmittedsimultaneously and having different destinations; deciding a firsttransmission time to be longest among the plurality of secondtransmission times; adding a second unit to the first unit to constructa third unit if a corresponding one of the second transmission times isshorter than the first transmission time, a transmission time of thethird unit resulting in a time equivalent to the first transmissiontime; generating one of the plurality of physical frames from the thirdunit and generating one of the plurality of physical frames from thefirst unit if corresponding one of the second transmission times isequal to the first transmission time; and transmitting a set of physicalframes simultaneously, where each physical frame in the set of thephysical frames has a different destination.
 2. A radio communicationmethod, comprising: generating a plurality of first units, each of thefirst units being generated by connecting a set of MAC Protocol DataUnits (MPDUs) and transmission destinations of MPDUs within a same oneof the first unit being identical; selecting a part of the plurality offirst units as a first set to be transmitted simultaneously, the firstunits in the first set each having a different MPDU transmissiondestination; deciding a longest one among a plurality of secondtransmission times as a first transmission time, by calculating theplurality of second transmission times on the first units in the firstset, where each of the second transmission times is a physical frametransmission time carrying each one of the first units in the first setand is calculated based on a length of each one of the first units and adata rate assigned to the physical frame transmission times carryingeach one of the first units; adding a variable second unit to each oneof the first units in the first set if a corresponding one of the secondtransmission times to each one of the first units in the first set isshorter than the first transmission time, each set of the one of thefirst units in the first set and the added variable second unit formingone of a plurality of third units, each physical frame transmission timecarrying each of the plurality of third units being calculated based ona length of each of the plurality of third units and a data rateassigned to each of the physical frames carrying each of the pluralityof third units, the data rate of each of the plurality of third unitsbeing equal to the data rate of the corresponding one of the first unitsin the first set, each of the physical frame transmission times carryingeach of the plurality of third units resulting in a time equivalent tothe first transmission time, and the first set changed to a second setof the first units from the first set which are to be transmitted in thefirst transmission time and the plurality of third units resulting inbeing transmitted in same physical frame transmission time with thefirst transmission time; generating a plurality of physical frames, eachof the plurality of physical frames being generated from each one of thefirst and third units in the second set; and transmitting the pluralityof physical frames simultaneously.
 3. A radio communication apparatus,comprising: a first generating device which generates a plurality offirst units, each of the first units being generated by connecting a setof MAC Protocol Data Units (MPDUs) and transmission destinations ofMPDUs within a same one of the first unit being identical; a selectiondevice which selects a part of the plurality of first units as a firstset to be transmitted simultaneously, the first units in the first seteach having a different MPDU transmission destination; a decision devicewhich decides a longest one among a plurality of second transmissiontimes as a first transmission time, by calculating the plurality ofsecond transmission times on the first units in the first set, whereeach of the second transmission times is a physical frame transmissiontime carrying each one of the first units in the first set and iscalculated based on a length of each one of the first units and a datarate assigned to a physical frame carrying each one of the first units;an addition device which adds a variable second unit to each one of thefirst units in the first set if a corresponding one of the secondtransmission times to each one of the first units in the first set isshorter than the first transmission time, each set of the one of thefirst units in the first set and the added variable second unit formingone of a plurality of third units, each physical frame transmission timecarrying each of the plurality of third units being calculated based ona length of each of the plurality of third units and a data rateassigned to each of the physical frames carrying each of the pluralityof third units, the data rate of each of the plurality of third unitsbeing equal to the data rate of the corresponding one of the first unitsin the first set, each of the physical frame transmission times carryingeach of the plurality of third units resulting in a time equivalent tothe first transmission time, and the first set changed to a second setof the first units from the first set which are to be transmitted in thefirst transmission time and the plurality of third units resulting inbeing transmitted in same physical frame transmission time with thefirst transmission time; a generation device which generates a pluralityof physical frames, each of the plurality of physical frames beinggenerated from each one of the first and third units in the second set;and a transmission device which transmits the plurality of physicalframes simultaneously.
 4. The apparatus according to claim 3, whereinthe transmission device transmits the plurality of physical framessimultaneously in accordance with a multi-user Multiple Input MultipleOutput (MIMO) system.
 5. The apparatus according to claim 3, wherein thetransmission device transmits the plurality of physical frames inaccordance with multi-channel communication which communicates with aplurality of radio terminals by using a plurality of channelssimultaneously.
 6. The apparatus according to claim 3, wherein theplurality of first units contain delimiter fields, each of the delimiterfields in the first units are located in front of each of the MPDUs, andwherein the addition unit adds the delimiter fields as the variablesecond unit to the first unit.
 7. The apparatus according to claim 6,wherein the variable second unit is added after the plurality of firstunits.
 8. The apparatus according to claim 3, wherein the variablesecond unit is a Quality of Service (QoS) Null frame having avariable-length Frame Body and the QoS Null frame is added after theplurality of first units.
 9. The apparatus according to claim 3, whereinthe variable second unit is a copy of one of the MPDUs which is locatedlast in the plurality of first units.
 10. The apparatus according toclaim 3, wherein the variable second unit is inserted between the MPDUsgenerating each one of the plurality of first units to make transmissioncompletion times of the MPDUs located at an end of each one of theplurality of first units in the second set which are to be transmittedin the first transmission time and the plurality of third units in thesecond set resulting in being transmitted in a same physical frametransmission time with the first transmission time to be the same. 11.The apparatus according to claim 3, wherein the variable second unit isa frame space.
 12. The apparatus according to claim 3, whereintransmission acknowledgement request frames are appended to the variablesecond unit.
 13. The apparatus according to claim 3, further comprisingan antenna, wherein the transmitting device is configured to transmitthe plurality of physical frames via the antenna.